In general, a rotating device such as a joint of a robot manipulator includes a driving unit such as a driving motor, a rotating shaft which is connected to the driving unit so as to deliver a rotating force, and a rotating member which is connected to the rotating shaft so as to rotate.
The rotating member is rotated about the rotating shaft by the rotating device, and a variety of operations are performed by the rotation of the rotating member.
In general, a rotating device such as a joint of a robot manipulator has limit torque which is applied to the rotating member serving as an output unit. However, an unexpected external force may be applied to the robot manipulator which comes in contact with the outside during an operation. When the rotating shaft and the rotating member are rigidly connected to each other, the rotating shaft is rotated continuously even when an external force is applied to the rotating member. On the other hand, the rotating member cannot be rotated because of the interference of the external force. As a result, torque equal to or greater than limit torque may be applied between the rotating shaft and the rotating member, and the device may be damaged. Further, when a person or an object comes in contact with the rotating member which is being rotated, the person or object may be hurt or damaged.
Therefore, when an external force equal to or greater than limit torque is applied to the rotating device, the person or object coming in contact with the rotating device needs to be protected, while the rotating device is protected.
To secure the stability of the rotating device, a coupling device has been proposed, in which a rotational displacement occurs above predetermined torque. That is, a rotating shaft and a rotating member are not rigidly connected to each other, but are separated above predetermined torque such that an independent rotational displacement occurs.
However, the conventional rotating device in which a rotational displacement occurs in the rotating shaft and the rotating member has a complex structure, and the weight of the rotating device increases inevitably because of the structure. Further, the rotating device does not have a function of returning to the initial position, after an external force is eliminated. Therefore, a separate sensor or control unit, which returns the rotating shaft and the rotating member to the initial position after a rotational displacement has been formed in the rotating shaft and the rotating member by an external force, should be additionally installed.